1. Field of the Invention
The invention relates to a computer tomograph detector for the detection of electromagnetic radiation transmitted by an object, which detector includes at least one detector row which consists of a plurality of detector elements, each detector element including a scintillator for converting radiation of a first energy level into radiation of a second energy level, as well as a photosensor for converting the radiation into an electrical current, an amplifier element being associated with each photosensor.
2. Description of Related Art
Computer tomographs serve to form planar images of imaginary slices of an object, for example a body. A computer tomograph generally consists of a circular portal frame or gantry in which a scanning device with an X-ray source is integrated. The scanning device rotates about an imaginary longitudinal axis extending through the body. After having traversed the body, the X-rays are incident on an oppositely situated detector which rotates together with the scanning device. The reconstruction of a single image requires a set of images which correspond to different protection angles, each image having radiation intensities which are detected by individual detector elements.
Detectors comprising one or more rows are known. EP 0 819 406 A1 discloses a computer tomograph with a plurality of parallel detector rows, i.e. a so-called multi-line detector. The detector consists of a two-dimensional array of detector elements, i.e. a plurality of detector rows, which are arranged parallel to one another in the direction of the axis of rotation (z direction). A multi-line detector offers the advantage that during a rotation of the gantry a plurality of cross-sectional images can be simultaneously picked up in dependence on the extent of the detector in the z direction.
In the case of a computer tomograph with a one-dimensional detector, i.e. single-line detector, only the cross-sectional image of a fan-shaped beam is picked up. In order to obtain a volume image, the body, i.e. the patient, must be moved through the computer tomograph. When a multi-line detector is used, however, a pyramid-like beam or cone beam is used, so that a volume image can be picked up already during a single rotation of the gantry, said volume image consisting of a number of cross-sectional images in conformity with the number of rows of the array.
The body is scanned helically or spirally in the case of single-line detectors as well as in the case of multi-line detectors. The gantry is then rotated about the body while at the same time the patient is moved along the axis of rotation relative to the gantry. Using a multi-line detector, the execution of such a spiral scan is significantly faster than when use is made of a single-line detector, because the patient can be transported over the full width of the detector during one revolution of the gantry. Such a reduction of the scanning time by using multi-line detectors minimizes the detrimental image artefacts due to motions of the patient, for example due to respiration or muscle contractions.
The multi-line detector which is known from EP 0 819 406 A1 concerns a two-dimensional array of detector elements, each of which is constructed on the basis of a ceramic scintillator which is succeeded by a photodiode. The detector signals are received by a multiplexer. The multiplexer applies the information to a computer and the images of the body are displayed on a monitor.
A computer tomograph provided with a two-dimensional array is also known from U.S. Pat. No. 5,291,402. As is customary in detectors of this kind, each detector element of the detector array is electrically independent. The signals of the decoupled detector elements are acquired by means of a data acquisition system. Those skilled in the art will know that such a data acquisition system requires a multitude of discrete amplifier elements which are associated with the individual detector elements.
It is a drawback that the relevant photodiodes are connected to the amplifier elements via individual supply leads. This leads to a very large number of connections, notably in the case of multi-line detectors. The high density of the connection leads may lead to crosstalk of the channels and irritations due to the coupling in of interference by capacitive and/or inductive coupling. This causes a high, undesirable electrical noise and a deterioration of the DQE (Detective Quantum Efficiency).
Citation of a reference herein, or throughout this specification, is not to construed as an admission that such reference is prior art to the Applicant's invention of the invention subsequently claimed.
Therefore, it is an object of the invention to provide a computer tomograph detector which may comprise a plurality of detector rows, involves less electronic noise and at the same time offers a higher DQE and fast preparation of the desired image.